Same as it is here…right as the forsythias flowers are falling to the ground which is right as the very first lilac flowers are opening.  Use these two shrubs a your clock…not a date on the calendar.  That way your timing is correct no matter whether we have an early (like 2012) or late (like this year) spring.  Trust the forsythia and lilacs in your area. Here’s a link to blog post all about that.